Transducer



June 23, 1964 c. D. SAMUELSON TRANSDUCER 2 Sheets-Sheet 2 Filed Nov.1'7, 1960 Jersey Filed Nov. 17, 1960, Ser. No. 69,851 1'2 Claims. (Cl.310-81) My invention relates to transducers and in particular to thosetransducers having more than one output and which are comprised of morethan one piezosensitive element.

In the prior art, it has been usual to manufacture transducers of asingle type of piezosensitive element. Such transducers have beendescribed in the literature and in many patents. Presently knowntransducers are made, for example, with various types of elements suchas quartz, Rochelle salts, ferroelectric ceramics, magnetostrictives,piezoresistives and electromechanically sensitive materials.

By an electromechanically sensitive material I mean one which changesone of its electrical and/ or one of its magnetic characteristics whensubjected to mechanical stress and by a piezosensitive element I meanone which changes one of its electrical characteristics when subjectedto mechanical stress. Some electromechanically sensitive materials andsome piezosensitive elements are reversible, that is, an electricaland/or magnetic signal applied thereto will produce a mechanical stresstherein. Other such materials are not reversible. For example,transducers or ferroelectric ceramic are reversible and those of othermaterials are not reversible, that is, no mechanical movement isproduced when an electrical signal is applied. I choose to designatethese latter materials and elements as single-ended or passivepiezosensitive or electromechanically sensitive materials. I choose tofurther designate the reversible piezosensitive materials as activepiezosensitive or electromechanically sensitive materials.

Examples of single-ended or passive piezosensitive materials are P-typeand N-type silicon semiconductors such as have been described in US.Patent No. 2,905,771 to Fred P. Burns, issued September 22, 1959. Thesemiconductors described by Burns are called piezoresistives becausetheir resistance changes when mechanical stress is applied. It should benoted that there are many other piezoresistive materials other thanthose described by Burns and in the present application and theteachings of my invention apply as well to these other piezoresistivematerials. Moreover, other piezosensitive materials may be used inpracticing the invention. These other piezosensitive materials are anyof those wherein one of the electrical characteristics changes when thematerial is subjected to a mechanical stress.

Piezoelectric materials such as quartz, Rochelle salt, polarizedierroelectric ceramics are active piezosensitive materials and aredesignated as piezoelectric because they generate an electric voltagewhen subjected to a mechanical stress. Piezoresistive materials, whichare passive, are designated as piezoresistive because the resistance ofthe material changes when it is subjected to a mechanical stress.Examples of piezoresistive materials are P-type or N-type silicon.

I have discovered that improved results can be obtained from phonographpickups, microphones, accelerometers and similar electromechanicaldevices when a plurality of outputs are obtained from a singlemechanical stress. There are many advantages to such devices since, forexample, it is possible to obtain different electrical outputcharacteristics from the same mechanical stress. By applying suitablephase and frequency shifts to one or more of the outputs with respect toeach other, it is pos- United States Patent 3,138,726 Patented June 23,1964 sible to produce stereophonic effects from a single microphone orphonograph pickup. This phonograph pickup stereo effect is obtained fromthe common monaural type records when using a pickup of my invention andassociated electronic equipment. Accelerometers made in accordance withmy invention have multiple outputs in a single unit so that if oneoutput fails, measurements may still be made. This is particularlyimportant in missiles, rockets and similar devices in which space is ata premium.

It is an important object of my invention to provide a transducer inwhich more than one electromechanically sensitive element is used.

It is a further object of my invention to provide such a transducerwherein one of the several electromechanically sensitive elements isused to produce a mechanical stress from an electrical signal andanother of the elements produces an electrical signal from themechanical stress.

It is a still further object of my invention to provide such atransducer wherein there are a plurality of usable electrical outputsavailable from a single mechanical stress.

These and other objects, advantages, features and uses will be apparentduring the course of the following description when taken in conjunctionwith the accompanying drawings wherein:

FIGURE 1 is a plan view of a preferred embodiment of my invention usedas a directly-monitored phonograph recorder and wherein the associatedcircuits are shown in block schematic,

FIGURE 2 is a view similar to that of FIGURE 1 of a further embodimentof my invention used as a directlymonitored phonograph recorder,

FIGURE 3 is a View similar to that of FIGURE 1 showing an embodimentsimilar to that of FIGURE 1 used as a stereophonic phonographreproducer,

FIGURE 4 is a view similar to that of FIGURE 1 showing an embodimentsimilar to: that of FIGURE 2 used as a stereophonic phonographreproducer,

FIGURE 5 is a view similar to that of FIGURE 1 showing a three channelstereophonic phonograph reproduc'er using a piezoelectric element andtwo single piezoresistive elements, and

FIGURE 6 is a view similar to that of FIGURE 1 showing a three channelstereophonic phonograph reproducer using a piezoelectric element and twodouble piezoresistive elements.

In the drawings, wherein, for the purpose of illustration, are shownseveral embodiments of devices of my invention, the numeral 10 generallydesignates a transducer used as a combined phonograph recorder andpickup. Transducer 10 is seen to comprise piezoelectric element 12,piezoresistive element 14, and stylus 16. Piezoelectric element 12 ispreferably formed of ferroelectric ceramic such as barium titanate, leadtitanate-zirconate, each with or without additives but may be formed ofany other natural or artificial piezoelectric material so long asapplication of an electrical signal thereto will produce motion ofstylus 16. Piezoresistive element 14 is preferably formed of P-typesilicon cut in the 1,1,1 direction. The designation 1,1,1 is inaccordance with the so-called Miller indices which are commonly used inthe crystallographic art. However, other piezoresistive materials suchas N-type silicon, P-type and N-type germanium, P-type and N-type indiumantimonide and similar materials may also be used. Moreover,piezosensitive materials other than the piezoresistives may be used inthe position of piezoresistive element 14.

Stylus 16 is affixed to the combination in accordance with the techniquetaught by Glenn N. Howatt in his United States Patent 2,640,165, issuedMay 26, 1953. Piezoelectric element 12 is seen to comprise ceramicstrips 18 and 20 to which are affixed electrodes 22, 24, 26 and 28 in amanner such as is taught in the aforementioned patent to Glenn N.HoWatt. In accordance with the said patents teachings, ceramic strips 18and 20 are suitably aifixed to flexible reinforcing plate which isformed of copper or similar material. Piezoresistive element 14 isaflixed to flexible reinforcing plate 32 by means of an epoxy resin andceramic strip 20 is affixed to flexible reinforcing plate 32, which isformed of similar material to that of plate 30, in the same manner asceramic strips 18 and 20 are affixed to flexible reinforcing plate 30.Ceramic strips 18 and 20 are oppositely polarized if they are to be usedconnected in series as shown in FIGURE 1 and are polarized in the samedirection if they are to be used connected in parallel.

Electrical connection is made between piezoelectric element 12 andrecording amplifier 36 by means of leads 34. Amplifier 36 has theappropriate gain and power output necessary to stress piezoelectricelement 12 when an acoustic wave is applied to microphone 38. ElectrodesY40 and 42 are painted on piezoresistive element 14 and leads 43 aresuitably affixed thereto. Battery 44, variable resistor 46 and theprimary of audio transformer 50 are connected in series withpiezoresistive element 14 through electrodes 40 and 42. It can readilybe seen that a change in the resistance of piezoresistive element 14will produce a change in current flow in the primary of transformer 50.This change in current flow in the primary of transformer 50 causes anA.-C. voltage to be induced in the secondary of transformer 50 whichvoltage is amplified in monitor amplifier 52. Amplifier 52 hassufficient gain and power output to amplify the signal from thesecondary of transformer St) and to deliver enough power to driveloudspeaker 54 or a similar device such as a pair of headphones. 7 Inoperation, the user of the transducer of FIGURE 1 may monitor the signalapplied to the recording medium by stylus 16 and thereby know of anyfailure instantaneously. Program is fed, for example, into microphone38. The signal is amplified in recording amplifier 36 whose output isapplied to piezoelectric element 12. This causes piezoelectric element12 to stress and thus moves stylus 16. The movement of stylus 16 on therecording medium thereby records the acoustic signal from themicrophone. The movement of piezoelectric element 12 also causespiezoresistive element 14 to stress in synchronism with the movement ofpiezoelectric element 12. As a result of this movement, the resistanceof piezoresistive element 14 is changed and an A.-C. signal is inducedin the secondary of transformer 50. This A.C. signal is amplified inmonitor amplifier 52 and heard in loudspeaker 54. It should be notedthat any other type of electroacoustic input may be substituted formicrophone 38. For example, a phonograph pickup, tape playback or theaudio output of a radio or television set may be used. Moreover,multiple audio inputs may be mixed ahead of the recording amplifier inany manner wellknown in the art.

The transducer of FIGURE 3 is similar to that of FIG- URE 1 but isconnected as a phonograph pickup which produces a stereophonic outputfrom a standard monaural record. 'The output of piezoresistive element14 is connected in series with battery 44, variable resistor 46 and theprimary of transformer 50 through leads 43 and electrodes 40 and 42. Thesecondary of transformer 50 is connected to the input of amplifier 56and thence to loudspeaker 62. The output of piezoelectric element 12 isfed through leads 34 to variable filter and phaseshift' network 58. Theoutput of variable filter and phaseshift network 58 is connected to theinput of amplifier 60 whose output is connected to loudspeaker 64.

' If desired, another variable filter and phase-shift network may beconnected between the secondary of transformer 50 and the input ofamplifier 56. In this manner, certain frequencies can be confined to onechannel and other frequencies can be confined to the other channel. Highpass, low pass or band pass filters may be used and the phase differencebetween the two channels may be adjusted to produce the most pleasingeffect for the listener. Standard phase-shift circuits, which arewell-known in the art, may be used to accomplish the desired results.Moreover, the variable filter and phase-shift network may be connectedat the output of the piezoresistive element instead of at the output ofthe piezoelectric element.

In operation, stylus 16 is moved by the grooves in the record beingreproduced thereby causing transducer 10 to stress. As a result of thisstress, piezoelectric element 12 and piezoresistive element 14 arestressed. An electrical signal appears at the input of amplifier 56 dueto the change in resistance of piezoresistive element 14 and a secondelectrical signal appears at the input of variable filter andphase-shift network 58 due to the piezoelectric effect in piezoelectricelement 12. By judicious location of loudspeakers 62 and 64 in the roomand adjustment of variable filter and phase-shift network 58, I havebeen able to produce excellent stereophonic eifects from monauralrecordings.

It should be noted that the transducers of my invention are theso-called benders, that is, the end opposite the stylus is clamped tothe pickup arm and the device is caused to bend while the clamped endremains fixed. Plates 30 and 32 serve to strengthen the transducers andthereby materially reduce the likelihood of cracking of the ceramic orthe crystal.

In FIGURE 2, there is shown a further embodiment of transducer of myinvention which is designated as 10 and wherein the piezoresistiveelement is designated as 14'. Piezoresistive element 14 comprises P-typesilicon elements 15 and 17 cut in the 1,1,1 direction and a central,flexible plate 19. Plate 19 serves to strengthen the combination andelements 15 and 17 are bonded thereto by means of an epoxy resin.Electrodes 40 are painted to elements 15 and 17 at one end thereof andelectrode 42a is applied to the other end of elements 15 and 17 and iscommon to both elements 15 and 17. Elements 15 and 17 are connected in abridge circuit with fixed resistor 47 and variable resistor 49 by meansof leads 43. Power is supplied to the bridge by battery 44 and thevarying output due to the change in resistance of elements 15 and 17 isapplied to the primary of transformer 50. To give mechanical strength tothe transducer 10', piezoelectric element 12 and piezoresistive element14' are affixed to flexible reinforcing plate 33 by means of an epoxyresin or similar adhesive. Plate 33 is formed of copper or similarmaterial and is similar to reinforcing plates 30 and 32. The secondaryof transformer 50 is connected to the input of variable filter andphase-shift network 51. The output of variable filter and phase-shiftnetwork 51 is connected to the input of amplifier 52 whose output isconnected to loudspeaker 54. I have shown variable filter andphase-shift network 51 in FIGURE 2 in order to demonstrate theflexibility obtainable when using transducers of my invention. It shouldbe noted that the embodiment of FIGURE 2 may be used without thevariable filter and phase-shift network 51.

The operation of the transducer of FIGURE 2 is similar to that of thetransducer of FIGURE 1. Piezoresistive element 14 is formed of twoelements connected in a bridge circuit to thereby produce greatersensitivity than can be obtained from the single element ofpiezoresistive 14. When the embodiment of FIGURE 2 is used withoutvariable filter and phase-shift network 51, the signal from microphone38 is monitored in loudspeaker 54. When the variable filter andphase-shift network is used, special filter effects may be obtained inloudspeaker 54 even though a normal audio input is applied to microphone38. By way of example but not by way of limitation, it is possible toproduce telephone long line transmission quality at the loudspeaker orto otherwise limit or accentuate certain frequencies in the audio range.

The transducer of FIGURE 2 may be connected as a stereophonic pickup asshown in FIGURE 4. The operation of the transducer is the same as thatof FIGURE 3 except for the bridge circuit which is used in connectionwith elements 15 and 17 instead of the series circuit which is used inconnection with element 14. It is to be noted that one variable filterand phase-shift network may be used instead of the two shown in thefigure in the manner I have described in connection with the embodimentof FIGURE 3.

In FIGURE 5, there is shown a still further embodiment of transducer ofmy invention in which there are three active elements. Transducer 10 isseen to comprise piezoelectric element 12 and two piezoresistiveelements 14 and 14a. Plates 30, 32 and 32a serve to strengthen thecombination as has been described above in connection with theembodiments of FIGURES 1 through 4. Electrodes 49 and 42 are painted onpiezoresistive element 14 and electrodes 49' and 42 are painted onpiezoresistive element 14a. Battery 44, variable resistor 46 and theprimary of transformer 50 are connected in series with piezoresistiveelement 14 by means of leads 43. Battery 44', variable resistor 46' andthe primary of transformer 50' are connected in series withpiezoresistive element 14"by means of leads 43'.

The secondary of transformer 50 is connected to variable filter andphase-shift network 70. The output of variable filter and phase-shiftnetwork 70 is connected to the input of amplifier 72 whose output isconnected to loudspeaker 74. The secondary of transformer 50 isconnected to variable filter and phase-shift network 70. The output ofvariable filter and phase-shift network 70 is connected to the inputamplifier 72 whose output is connected to loudspeaker 74. The output ofpiezoelectric element 12 is fed to variable filter and phase-shiftnetwork 58 by means of leads 34. The output of variable filter andphase-shift network 58 is connected to the input of amplifier 60. Theoutput of amplifier 60 is connected to loudspeaker 64.

I have found that better stereo effects are obtained from a threechannel system such as is illustrated in FIGURE than from the twochannel systems illustrated in FIGURES 3 and 4. The three speakers maybe placed in the room and the filter and phase-shift net- 'worksadjusted so that the maximum of audio presence is obtained. Moreover,the flexibility of adjustment per- .mits the user to vary thereproduction of the monaural records to suit his own taste.

In FIGURE 6, transducer 11 is seen to comprise piezoelectric element 12and piezoresistive elements 14' and 14a. Piezoresistive elements 14' and14a are similar .to piezoresistive element 14 of FIGURES 2 and 4.Piezoresistive element 14 comprises piezoresistive elements 15 and 17and plate 19 and piezoresistive element 14a comprises piezoresistiveelements 15' and 17' and plate 19'. Electrodes 4d and 42a are applied topiezoresistive element 14' and electrodes 40' and 42a are applied topiezoresistive element 14a. Resistor 47 and variable resistor 49 areconnected in a bridge circuit with piezoresistive elements 15 and 17 bymeans of leads 43. Battery 44 supplies power to the bridge and itsoutput is connected to the primary of transformer 50. Resistor 47 andvariable resistor 49 are connected in a bridge circuit withpiezoresistive elements 15' and 1'7" by means of leads 43". Battery 44supplies power to the bridge and its output is connected to the primaryof transformer 50'.

The secondary of transformer 50 is connected to variable filter andphase-shift network 7%) whose output is connected to the input ofamplifier 72. The output of amplifier 72 is connected to loudspeaker 74.The secondary of transformer 50' is connected to variable filter andphase-shift network 70' whose output is connected to the input ofamplifier 72'. The output of amplifier 72 is connected to loudspeaker74'. The output of piezoelectric element 12 is fed by means of leads 34to variable filter and phase-shift network 58 whose output is connectedto the input of amplifier 60. The output of amplifier 653 is connectedto loudspeaker 64.

The embodiment of FIGURE 6 has increased sensitivity over that of FIGURE5 and is operated as a three channel system with results which aresimilar to those described for the embodiment of FIGURE 5.

While I have shown the filter and phase-shift network as a singleelement placed between the electromechanically sensitive element and theamplifier in all the illustrations, it is also within the contemplationof my invention to use separate filter and/or phase-shift networks atany suitable place in the system.

While I have disclosed my invention in relation to specific examples andin specific embodiments, I do not wish to be limited thereto, forobvious modifications will occur to those skilled in the art withoutdeparting from the spirit and scope of my invention.

Having thus described my invention, I claim:

1. A transducer comprising a pair of thin strips of piezoelectricceramic, a metal strip, an electrode applied to each surface of each ofsaid thin strips of piezoelectric ceramic, said thin strips ofpiezoelectric ceramic being afiixed to said metal strip such thatelectrical and mechanical contact is made between an electrode on eachof said thin strips of piezoelectric ceramic and said metal strip, athin strip of piezoresistive material, a pair of electrodes applied tosaid thin strip of piezoresistive material, said thin strip ofpiezoresistive material being affixed to one of said thin strips ofpiezoelectric ceramic on the surface thereof opposite that affixedtosaid metal strip, means for making electrical connection to theelectrodes applied to said thin strips of piezoelectric ceramic, andmeans for making electrical connection to the electrodes applied to saidthin strip of piezoresistive material.

2. A transducer comprising a pair of thin strips of piezoelectricceramic, a first metal stri an electrode applied to each surface of eachof said thin strips of piezoelectric ceramic, said thin strips ofpiezoelectric ceramic being aflixed to said first metal strip such thatelectrical and mechanical contact is made between an electrode on eachof said thin strips of piezoelectric ceramic and said first metal strip,a pair of thin strips of piezoresistive material, a pair of electrodesapplied to each of said thin strips of piezoresistive material, a secondmetal strip, said thin strips of piezoresistive material being aflixedto each surface of said second metal strip such that said second metalstrip is mounted between said thin strips of piezoresistive material,one outer surface of one of said thin strips of piezoelectric ceramicbeing affixed to one outer surface of one of said thin strips ofpiezoresistive material, means for making electrical connection to the'electrodes applied to said thin strips of piezoelectric ceramic, andmeans for making electrical connection to the electrodes applied to saidthin strips of piezoresistive material.

3. An electromechanical device comprising a pair of thin strips ofpiezoelectric ceramic, a metal strip, an electrode applied to eachsurface of each of said thin strips of piezoelectric ceramic, said thinstrips of piezoelectric ceramic being affixed to said metal strip suchthat electrical and mechanical contact is made between an electrode oneach of said thin strips of piezoelectric ceramic and said metal strip,a thin strip of piezoresistive material, a pair of electrodes applied tosaid thin strip of piezoresistive material, said thin strip ofpiezoresistive material being afiixed to one of said thin strips ofpiezoelectric ceramic on the surface thereof opposite that affixed tosaid metal strip, means for making electrical connection to theelectrodes applied to said thin strips of piezo electric ceramic, meansfor making electrical connection to the electrodes applied to the thinstrip of piezoresistive material, means for applying mechanical stressto the combination, a first amplifier connected to the electrodesapplied to said thin strips of piezoelectric ceramic, a source ofvoltage, a resistor, and a second amplifier, said source of voltage,said resistor and said second amplifier being 4. An electromechanicaldevice as described in claim 3 including phase-shifting means connectedto the input of i said second amplifier.

5. An electromechanical device as described in claim 3 including filtermeans connected to the input of said second amplifier.

6. An electromechanical device comprising a pair of thin strips ofpiezoelectric ceramic, a metal strip, an electrode applied to eachsurface of each of said thin strips of piezoelectric ceramic, said thinstrips of piezoelectric ceramic being aflixed to said metal strip suchthat electrical and mechanical contact is made between an electrode oneach of said thin strips of piezoelectric ceramic and said metal strip,a thin strip of piezoresistive material, a pair of electrodes applied tosaid thin strip of piezoresistive material, said thin strip ofpiezoresistive material being aflixed to one of said thin strips ofpiezoelectric ceramic on the surface thereof opposite that afiixed tosaid metal strip, means for making electrical connection to theelectrodes applied to said thin strips of piezoelectric ceramic, meansfor making electrical connection to the electrodes applied to the thinstrip of piezoresistive material, means for applying electricalexcitation tosaid thin strips of piezoelectric ceramic connected to theelectrodes applied to said thin strips of piezoelectric ceramic andamplifying means connected to the electrodes applied to the thin stripof piezoresistive material.

7. An electromechanical device comprising a pair of thin strips ofpiezoelectric ceramic, a first metal strip, an electrode applied to eachsurface of each of said thin strips of piezoelectric ceramic, said thinstrips of piezoelectric ceramic being affixed to said first metal stripsuch that electrical and mechanical contact is made between an thinstrips of piezoresistive material, one outer surface of one of said thinstrips of piezoelectric ceramic being aflixed to one outer surface ofone of said thin strips of piezoresistive material, means for makingelectrical connection to the electrodes applied to said. thin strips ofpiezoelectric ceramic, means for making electrical connection to theelectrodes applied to said thin' strips of piezoresistive material,means for applying mechanical stress to the combination, a firstamplifier connected to the electrodes applied to said thin strips ofpiezoelectric ceramic, a source of voltage, a first resistor, a secondresistor and a second amplifier, said source of voltage, said firstresistor, said second resistor, and said second amplifier beingconnected to the electrodes applied to said thin strip of piezoresistivematerial such that said thin strips of piezoresistive material form twoarms of a bridge circuit and said first resistor and said secondresistor form the other two arms of said bridge circuit, said source ofvoltage being connected to two opposite terminals of said bridge circuitand the input of said second amplifier being connected to the other twoterminals of said bridge circuit.

8. An electromechanical device as described in claim 7 includingphase-shifting means connected between the bridge circuit'and the inputof said second amplifier.

9. An electromechanical device as described in claim 7 including filtermeans connected between the bridge circuit and the input of said secondamplifier.

10. An electromechanical device comprising a pair of thin strips ofpiezoelectric ceramic, a first metal strip, an

electrode applied to each surface or each of said thin strips ofpiezoelectric ceramic, said thin strips of piezoelectric ceramic beingafiixed to said first metal strip such that electrical and mechanicalcontact is made between an electrode on each of said thin strips ofpiezoelectric ceramic and said first metal strip, a pair of thin stripsof piezoresistive material, a pair of electrodes applied to each of saidthin strips of piezoresistive material, a second metal strip, said thinstrips of piezoresistive material being affixed to each surface of saidsecond metal strip such that said second metal strip is mounted betweensaid thin strips of piezoresistive material, one outer surface of one ofsaid thin strips of piezoelectric ceramic being afiixed to one outersurface of one of said thin strips of piezoresistive material, means formaking electrical connection to the electrodes applied to said thinstrips of piezoelectric ceramic, means for making electrical connectionto the electrodes applied to said thin strips of piezoresistivematerial, means for applying electrical excitation to said thin stripsof piezoelectric ceramic connected to the electrodes applied to saidthin strips of piezoelectric ceramic and amplifying means connected tothe electrodes applied to the thin strip of piezoresistive material.

11. A transducer comprising a pair of thin strips of piezoelectricceramic, an electrode applied to each surface of said thin strips ofpiezoelectric ceramic, a metal strip, said thin strips of piezoelectricceramic being affixed to said metal strip such that electrical andmechani- -cal contact is made between an electrode on each of saidelectrodes applied to each of said pair of thin strips of piezoresistivematerial, one of said pair of thin strips of piezoresistive materialbeing affixed to the outer surface of one of said thin strips ofpiezoelectric ceramic, the other of said pair of thin strips ofpiezoresistive material being affixed to the outer surface of the otherof said thin strips of piezoelectric ceramic, means for makingelectrical connection to the electrodes applied to said thin strips ofpiezoelectric ceramic, and means for making electrical connection to theelectrodes applied to said pair of thin strips of piezoresistivematerial.

12. A transducer comprising a pair of thin strips of piezoelectricceramic, a first metal strip, an electrode applied to each surface ofeach of said thin strips of piezoelectric ceramic, said thin strips ofpiezoelectric ceramic being afiixed to said first metal strip such thatsaid first metal strip is mounted between said pair of thin strips ofpiezoelectric ceramic and such that said first metal strip makeselectrical and mechanical contact with the electrodes on the innersurfaces of said thin strips of piezoelectric material, two pairs ofthin strips of piezoresistive material, a pair of electrodes applied toeach of said thin strips of piezoresistive material, a second metalstrip, a third metal strip, one of said pairs of thin strips ofpiezoresistivematerial being afiixed to said second metal strip suchthat said second metal strip is motmted therebetween, the other of saidpairs of thin strips of piezoresistive material being afiixed to saidthird metal strip such that said third metal strip is mountedtherebetween, said pairs of thin strips of piezoresistive material beingaifixed to said pair of thin strips of piezoelectric ceramic such thatsaid pair of thin strips of piezoelectric ceramic are mounted betweensaid pairs of thin strips of piezoresistive material, means for makingelectrical connection to the electrodes applied to said thin strips ofpiezoelectric ceramic, and means for making electrical connection to theelectrodes applied to said thin strips of piezoresistive material.

References Cited in the file of this patent UNITED STATES PATENTS2,728,222 Becker et al Dec. 27, 1955

7. AN ELECTROMECHANICAL DEVICE COMPRISING A PAIR OF THIN STRIPS OFPIEZOELECTRIC CERAMIC, A FIRST METAL STRIP, AN ELECTRODE APPLIED TO EACHSURFACE OF EACH OF SAID THIN STRIPS OF PIEZOELECTRIC CERAMIC, SAID THINSTRIPS OF PIEZOELECTRIC CERAMIC BEING AFFIXED TO SAID FIRST METAL STRIPSUCH THAT ELECTRICAL AND MECHANICAL CONTACT IS MADE BETWEEN AN ELECTRODEON EACH OF SAID THIN STRIPS OF PIEZOELECTRIC CERAMIC AND SAID FIRSTMETAL STRIP, A PAIR OF THIN STRIPS OF PIEZORESISTIVE MATERIAL, A PAIR OFELECTRODES APPLIED TO EACH OF SAID THIN STRIPS OF PIEZORESISTIVEMATERIAL, A SECOND METAL STRIP, SAID THIN STRIPS OF PIEZORESISTIVEMATERIAL BEING AFFIXED TO EACH SURFACE OF SAID SECOND METAL STRIP SUCHTHAT SAID SECOND METAL STRIP, IS MOUNTED BETWEEN SAID THIN STRIPS OFPIEZORESISTIVE MATERIAL, ONE OUTER SURFACE OF ONE OF SAID THIN STRIPS OFPIEZOELECTRIC CERAMIC BEING AFFIXED TO ONE OUTER SURFACE OF ONE OF SAIDTHIN STRIPS OF PIEZORESISTIVE MATERIAL, MEANS FOR MAKING ELECTRICALCONNECTION TO THE ELECTRODES, APPLIED TO SAID THIN STRIPS OFPIEZOELECTRIC CERAMIC, MEANS FOR MAKING ELECTRICAL CONNECTION TO THEELECTRODES APPLIED TO SAID THIN STRIPS OF PIESORESISTIVE MATERIAL, MEANSFOR APPLYING MECHANICAL STRESS TO THE COMBINATION, A FIRST AMPLIFIERCONNECTED TO THE ELECTRODES APPLIED TO SAID THIN STRIPS OF PIEZOELECTRICCERAMIC, A SOURCE OF VOLTAGE, A FIRST RESISTOR, A SECOND RESISTOR AND ASECOND AMPLIFIER, SAID SOURCE OF VOLTAGE, SAID FIRST RESISTOR, SAIDSECOND RESISTOR, AND SAID SECOND AMPLIFIER BEING CONNECTED TO THEELECTRODES APPLIED TO SAID THIN STRIP OF PIEZORESISTIVE MATERIAL SUCHTHAT SAID THIN STRIPS OF PIEZORESISTIVE MATERIAL FROM TWO ARMS OF ABRIDGE CIRCUIT AND SAID RESISTOR AND SAID SECOND RESISTOR FORM THE OTHERTWO ARMS OF SAID BRIDGE CIRCUIT, SAID SOURCE OF VOLTAGE BEING CONNECTEDTO TWO OPPOSITE TERMINALS OF SAID BRIDGE CIRCUIT AND THE INPUT OF SAIDSECOND AMPLIFIER BEING CONNECTED TO THE OTHER TWO TERMINALS OF SAIDBRIDGE CIRCUIT.